Detecting an underground object

ABSTRACT

In a method of detecting an underground object which is at least partially under a surface of ground, a first view of the object determined by transmitting a first radar signal from a first known geolocation. A second view of the object is determined by transmitting a second radar signal from a second known geolocation. The respective first and second trajectories of the first and second radar signals are oblique with respect to the surface of the ground and the respective first and second trajectories are at a first angle with respect to each other. A position of the object is estimated by maximizing a correlation between the first view and the second view by adjusting an estimated dielectric constant associated with medium between the object and the surface of the ground.

BACKGROUND

Excavation is often done to expose an underground object, such as apipe, for maintenance or replacement. Digging as close to the objectbeing sought with automated digging machines, such as back hoes,maximizes the efficiency of excavation. However, if the location of theobject is not determined accurately enough, damage may occur.Furthermore, there may be other objects to be avoided in the excavationprocess, even if the excavation isn't exposing existing infrastructure.If the objects underground are not known or adequately located, theexcavation team may have to limit the use of automated digging equipmentto avoid damaging the objects, and spend a significant amount of timemanually digging with shovels.

One solution to this problem has been to use injected radiation. In thisprocess, an RF signal is injected into the object at a place where itbreaks the surface, and the rest of the object, typically a pipe istracked by a device on the surface that is sensitive of the radiatedsignal. However, injected radiation requires a portion of the object tobe exposed above the ground's surface so can be energized, and alsorequires the object to be conductive.

Another solution to this problem involves Ground Penetrating Radar (GPR)in which the radar signals are transmitted into the ground at aperpendicular angle. GPR is sensitive to a broader range of objects asit relies only on differences in dielectric constant between the objectand the surrounding ground to generate returns, which is not limited toconductive objects. However, this technique has not always providedadequate resolution or accurate depth measurements of the objects in theground.

An alternative GPR method utilizes an array of antenna positions from asingle point of view in order to form a synthetic aperture, typicallyfrom an oblique angle. The oblique angle is used primarily to enable thearray of antenna positions to be made uniform by employing an antennastructure, which would be cumbersome if done at while wheeled or towedalong the ground as occurs with the standard form of GPR. Syntheticaperture improves accuracy and resolution somewhat from standard GPR,but not to the degree needed in excavation work.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis application, illustrate embodiments of the subject matter, andtogether with the description of embodiments, serve to explain theprinciples of the embodiments of the subject matter. Unless noted, thedrawings referred to in this brief description of drawings should beunderstood as not being drawn to scale.

FIG. 1 depicts a perspective view of a technique for taking two views ofan underground object, according to one embodiment.

FIG. 2 depicts a radar head, according to one embodiment.

FIG. 3 depicts a perspective view of a technique for taking three viewsof an underground object, according to one embodiment.

FIG. 4 depicts a perspective view of a technique for taking four viewsof an underground object, according to one embodiment.

FIG. 5 depicts radar signals and angles between air paths associatedwith the radar signals according to one embodiment.

FIGS. 6 and 7 depict two different types of devices that can be used forsynthesizing a large aperture, according to various embodiments.

FIG. 8 depicts a block diagram of a system for detecting an object thatis under the ground, according to one embodiment.

FIG. 9 is a flow chart of a method of detecting an underground object,according to one embodiment.

DESCRIPTION OF EMBODIMENTS

Reference will now be made in detail to various embodiments, examples ofwhich are illustrated in the accompanying drawings. While the subjectmatter will be described in conjunction with these embodiments, it willbe understood that they are not intended to limit the subject matter tothese embodiments. On the contrary, the subject matter described hereinis intended to cover alternatives, modifications and equivalents, whichmay be included within the spirit and scope as defined by the appendedclaims. In some embodiments, all or portions of the electronic computingdevices, units, and components described herein are implemented inhardware, a combination of hardware and firmware, a combination ofhardware and computer-executable instructions, or the like. Furthermore,in the following description, numerous specific details are set forth inorder to provide a thorough understanding of the subject matter.However, some embodiments may be practiced without these specificdetails. In other instances, well-known methods, procedures, objects,and circuits have not been described in detail as not to unnecessarilyobscure aspects of the subject matter.

Notation and Nomenclature

Unless specifically stated otherwise as apparent from the followingdiscussions, it is appreciated that throughout the present Descriptionof Embodiments, discussions utilizing terms such as “determining,”“approximating,” “estimating,” “correlating,” or the like, often (butnot always) refer to the actions and processes of a computer system orsimilar electronic computing device. The electronic computing devicemanipulates and transforms data represented as physical (electronic)quantities within the electronic computing device's processors,registers, and/or memories into other data similarly represented asphysical quantities within the electronic computing device's memories,registers and/or other such information storage, processing,transmission, or/or display components of the electronic computingdevice or other electronic computing device(s).

Overview of Discussion

According to various embodiments, a method and system are provided fordetecting an object that is under the surface of the ground. One of theproblems with underground radar detection is that the cross section ofthe underground object may be too small compared with the wavelength ofthe radar signal to provide adequate resolution. Some radars use a widearray of frequencies to improve detection, however the shorterwavelengths capable of detecting smaller objects do not penetrate intothe ground well. Detecting and resolving long narrow items, such aspipes, can be compromised if the view from radar happens to be end-on tothe pipe.

Another limitation in underground radar location is accuracy. Even ifthe position of the radar unit is precisely known, locating theunderground object depends on the time-of-flight or phase shift of theradar signal. This signal velocity measurement is a function of thedielectric constant of the ground. Since the dielectric constant of theground is not well known through the volume, the accuracy of theobject's position is only as good as the estimate of the dielectricconstant.

According to various embodiments, improved accuracy or improvedresolution, or a combination thereof, with respect to legacy techniquesof detecting an object is provided. Improved accuracy here refers tobetter determination of the three dimensional location of the objectwith respect to a known frame of reference. The location of the objectincludes how far the object is under the ground's surface (also referredto herein as “depth”), among other things. Improved resolution pertainsto the ability to know that an underground object is present. Improvedaccuracy, improved resolution, or improved accuracy and resolution shallbe referred to herein as “improved detection.”

Improved detection can be provided by taking at least two views of theobject from different geolocations, according to various embodiments.For example, improved resolution and improved accuracy can be providedby taking two views of an object where the trajectories of the radarsignals for the respective views form an angle that is approximately 90degrees. Accuracy can be improved further by taking a third or fourthview of the object that form respective angles of approximately 180degrees and 270 degrees with respect to the first radar signal.

Viewing the object at 90 degrees, or some other angle not close to theoriginal view or 180 degrees, ensures that a long narrow object, such asa pipe, will have at least one long cross section in view of the radarand thus be detected.

Information pertaining to the views, particularly views that are 180degrees from one another can be used to better estimate a dielectricconstant of the medium between the surface of the ground and theunderground object. If the ground is made of more than one type ofmaterial, the information pertaining to the views can be used as an aidin estimating dielectric constants for each of the materials.

The one or more dielectric constants can be used as a part of estimatingthe velocity at which a radar signal traveled through the ground. Thevelocity estimate can be used as a part of estimating the location ofthe object in the ground. The improved estimation of dielectric constantdirectly improves that accuracy of the underground object location.

Multiple Views of an Object

FIG. 1 depicts a perspective view of a technique for taking two views ofan underground object, according to one embodiment.

FIG. 1 depicts a volume 122 that is below the surface 114 of the ground.This volume 122 is referred to as a “subsurface volume 122.” Thesubsurface volume 122 is defined by an x-axis, a y-axis and a z-axis. Asdepicted in FIG. 1, the length of the subsurface volume 122 is definedby the x-axis, the width of the subsurface volume 122 is defined by they-axis, and the depth of the subsurface volume 122 is defined by thez-axis.

An object 120 is located in the subsurface volume 122. It may be knownthat the object 120 is somewhere within the subsurface volume 122.However, it may not be known that the object 120 is somewhere within thesubsurface volume 122. Further, it may be known that a first object 120is within the subsurface volume 122 and while the first object 120 isbeing processed, according to various embodiments, a second object thatwas not previously known may be discovered.

Two views of the object 120 can be taken from the respective first andsecond geolocations 104 a, 104 b. More specifically, a first view of theobject 120 can be obtained using a radar head 102 positioned at thefirst geolocation 104 a and a second view of the object 120 can beobtained using the radar head 102 positioned at the second geolocation104 b. By “geolocation,” what is meant is a location known in threedimensions with respect to a common frame of reference to other objects.Thus, as utilized herein, geolocation 104 is a location known in threedimensions, which may be expressed with three-dimensional coordinates(e.g., x, y, and z coordinates).

Referring to FIG. 2, the radar head 102 can include a transmitting radarantennae 210 a and a receiving radar antennae 210 b, according to oneembodiment. The radar head 102 may or may not be a part of a SyntheticAperture Radar (SAR) device, as discussed herein.

Returning to FIG. 1, a first radar signal 106 a can be transmitted fromthe transmitting radar antennae 210 b located at the first geolocation104 a. The first radar signal 106 a can travel through the air along atrajectory as indicated by the air path 108 a. The first radar signal106 a can enter the ground at location 112 a where it intercepts thesurface 114 of the ground. According to one embodiment, informationdescribing the contour of the ground's surface 114 is used as a part ofestimating where the radar signal 106 a intercepted 112 a the surface114 of the ground. The angle 118 a of the transmitted radar signal 106 awith respect to the ground's surface 114 and information pertaining tothe contour of the ground's surface 114 can be used to estimate wherethe radar signal 106 a intercepted 112 a the ground's surface 114.

The first radar signal 106 a can travel along the earth path 110 a andintercept the object 120 at location 113 a, which causes the first radarsignal 106 a to be reflected back. The receiving radar antennae 210 bcan receive the reflected radar signal 106 a for the first view at thefirst geolocation 104 a.

According to one embodiment, “information describing a view” includes,but is not limited to, the angle 118 a between the transmitted radarsignal 106 a and the ground's surface 114, the length of the air path108 a for that radar signal 106 a, and the time between the time oftransmission of the radar signal 106 a and the time the reflected radarsignal 106 a returned.

The radar head 102 can be moved to the second geolocation 104 b wheresimilar processing can be performed to obtain a second view. Morespecifically, a second radar signal 106 b can be transmitted from thetransmitting radar antennae 210 a located at the second geolocation 104b. The second radar signal 106 b can travel through the air along atrajectory as indicated by the second air path 108 b. According to oneembodiment, the trajectory of the air path 108 a for the first radarsignal 106 a and the trajectory of the air path 108 b for the secondradar signal 106 b form an angle that is approximately 90 degrees. Thesecond radar signal 106 b can enter the ground's surface 114 at location112 b where it intercepts the surface 114 of the ground.

The second radar signal 106 b can then travel along the earth path 110 band intercept the object 120 at location 113 b, which causes the secondradar signal 106 b to be reflected back. The receiving radar antennae210 b can receive the reflected radar signal 106 b for the second viewat the second geolocation 104 b.

In order to maximize the power of the radar signals 106 that enter theground, according to one embodiment, trajectories of the radar signals106 a, 106 b for the respective geolocations 104 a, 104 b formapproximate Brewster angles 118 a, 118 b with respect to the ground'ssurface 114.

The subsurface volume 122 may be made of a homogenous medium or may bemade of a heterogeneous medium. An example of a homogenous medium is amedium made of one type of material. An example of a heterogeneousmedium is a medium made of different types of materials. Morespecifically, the subsurface volume 122 may be made of layers ofdifferent types of material where examples of the layers are asphalt,gravel, a mixture of gravel and dirt, dirt, clay, among other things. Alayer may be made of a mixture of materials. Each of the types ofmaterials or layers of materials has a dielectric constant. According toone embodiment, approximations of each of the respective dielectricconstants for each of the layers in the medium are determined, as willbecome more evident.

According to one embodiment, a third or fourth view can be obtained ofthe object 120 as a part of improving accuracy or improving resolution.FIG. 3 depicts a perspective view of a technique for taking three viewsof an underground object 120, according to one embodiment. For example,a third view can be taken from a third geolocation 104 c as depicted inFIG. 3 using various embodiments as discussed herein.

More specifically, the radar head 102 can be moved to the thirdgeolocation 104 c where similar processing can be performed to obtain athird view. A third radar signal 106 c can be transmitted from thetransmitting radar antennae 210 a from the third geolocation 104 c. Thethird radar signal 106 c can travel through the air along a trajectoryas indicated by the third air path 108 c. According to one embodiment,the trajectory of the air path 108 a for the first radar signal 106 aand the trajectory of the air path 108 c for the third radar signal 106c form an angle that is approximately 180 degrees. The third radarsignal 106 c can enter the ground's surface 114 at location 112 c whereit can intercept the surface 114 of the ground.

The third radar signal 106 c can travel along the earth path 110 c andintercept the object 120 at location 113 c, which causes the third radarsignal 106 c to be reflected back. The receiving radar antennae 210 bcan receive the reflected radar signal 106 c for the third view at thethird geolocation 104 c.

FIG. 4 depicts a perspective view of a technique for taking four viewsof an underground object 120, according to one embodiment. For example,a fourth view can be taken from a fourth geolocation 104 d as depictedin FIG. 4 using various embodiments as discussed herein.

More specifically, the radar head 102 can be moved to the fourthgeolocation 104 d where similar processing can be performed to obtain afourth view. A fourth radar signal 106 d can be transmitted from thetransmitting radar antennae 210 a from the fourth geolocation 104 d. Thefourth radar signal 106 d can travel through the air along a trajectoryas indicated by the fourth air path 108 d. According to one embodiment,the trajectory of the air path 108 a for the first radar signal 106 aand the trajectory of the air path 108 d for the fourth radar signal 106d form an angle that is approximately 270 degrees. The fourth radarsignal 106 d can enter the ground at location 112 d where it interceptsthe surface 114 of the ground.

The fourth radar signal 106 d can travel along the earth path 110 d andcan intercept the object 120 at location 113 d, which causes the fourthradar signal 106 d to be reflected back. The receiving radar antennae210 b can receive the reflected radar signal 106 d for the fourth viewat the fourth geolocation 104 d.

According to various embodiments, chirp or linear FM modulation that isa function of the wave lengths is used for one or more of the radarsignals.

According to one embodiment, information describing each of the views isobtained. For example, the information describing a view can include theangle 118 between the transmitted radar signal 106 and the ground'ssurface 114, the length of the air path 108 for that radar signal 106,and the amount of time from transmission to reception of a radar signal106, among other things.

As will become more evident, the information describing each of theviews can be correlated with each other to estimate one or moredielectric constants. The one or more dielectric constants can be usedto estimate one or more velocities of the radar signals 106 through oneor more layers of material between the ground's surface 114 and theobject 120, which in turn can be used to better estimate the location ofthe object 120 in the ground.

According to one embodiment, any two or more of the views of the object120 can be used to obtain a three dimensional (3D) picture of the object120.

An Object

Referring to FIGS. 1, 3 and 4, according to one embodiment, the object120, according to various embodiments, is made of a material that has adifferent dielectric constant than the medium that is between it and theground's surface 114. The difference between the respective dielectricconstants, according to one embodiment, is used for locating the object120.

According to another embodiment, the object 120 has a dielectricconstant that is close to the medium's dielectric constant. For example,a pipe made of PVC typically has a dielectric constant that is close tothat of the earth. However, embodiments are well suited for locating anobject 120, such as a PVC pipe, provided it contains another material,such as water, air or oil, which has a different dielectric constantthan earth.

It may be known that an object 120 is somewhere within the subsurfacevolume 122 prior to the first view, second view, third view or fourthview. However, it may not have been known that an object 120 wasanywhere within the subsurface volume 122 prior to obtaining any of theviews.

In some embodiments may have been known that an object 120 was in thesubsurface volume 122 prior to the fourth view but not known prior tothe third view. Likewise, it may have been known that the object 120 wasin the subsurface volume 122 prior to the third view but not known priorto the second view and so on.

In other embodiments, the existence of object 120 in subsurface volume122 may be known after, for example the second view, however the thirdview, fourth view, etc. allow for better dielectric constant estimation,leading to better accuracy with respect to the geolocation of object 120by allowing a previous estimation of the dielectric constant to berefined through the correlation of information from additional views.

Further, it may be known that a first object is within the subsurfacevolume 122 and while the first object is being processed, according tovarious embodiments, a second object, which was not previously known,may be discovered. For example, it may be known that the first objectwas within the subsurface volume 122 prior to any one of the views and asecond previously unknown object may be discovered during any one of theviews.

Angle Between Radar Signal and Ground's Surface

Referring to FIGS. 1, 3, and 4, according to one embodiment, the angle118 between each of the radar signals 106 and the ground's surface 114is an oblique angle. An oblique angle, according to one embodiment, isan angle that is not perpendicular to the ground's surface 114.

According to one embodiment, an angle 118 between a radar signal 106 andthe ground surface 114 is approximately a Brewster angle in order tomaximize the power of the radar signal 106 entering the ground. Forexample, the Brewster angle is an angle at which one of thepolarizations cancels itself out resulting in close to all of a radarsignal 106 being refracted into the ground.

Angle Between Radar Signals

FIG. 5 depicts radar signals and angles between air paths associatedwith the radar signals according to one embodiment. For example, FIG. 5depicts the first, second, third and fourth radar signals 106, accordingto one embodiment, and a first angle 116 a between the first and secondair paths 108 a, 108 b, a second angle 116 b between the first and thirdair paths 108 a, 108 c, and a third angle 116 c between the first andfourth air paths 108 a, 108 d. According to one embodiment, the firstangle 116 a is approximately 90 degrees, the second angle 116 b isapproximately 180 degrees, and the third angle 116 c is approximately270 degrees.

Although various embodiments are described with respect to angles 116between respective trajectories as indicated by the air paths 108 thatare approximately 90 degrees, 180 degrees, 270 degrees, variousembodiments are well suited to other angles. For example, according toone embodiment, the first angle 116 a may range between 20 degrees and160 degrees or between 200 and 340 degrees. According to anotherembodiment, the first angle 116 a may range from 20 degrees to 135degrees, the second angle 116 b may range from 135 degrees to 225degrees, and the third angle 116 c may range from 225 degrees to 340degrees.

Planes

Referring to FIGS. 1, 3, 4 and 5, according to one embodiment, thegeolocations 104 are located in a plane that is approximatelyhorizontal. The angles 116 a-116 c (FIG. 5) may be formed by movingclock wise or counter clock wise in the plane that is approximatelyhorizontal, according to one embodiment. However, embodiments are wellsuited for planes at other orientations. For example, the plane may beperpendicular to the ground's surface 114 or at a 45 degree angle of theground's surface 114, among other things. Embodiments are well suitedfor planes that are at any angle with respect to the ground's surface114. Further, embodiments are well suited for using more than one plane.For example, the first geolocation 104 a and the second geolocation 104b may be in a first plane while the third and fourth geolocations 104 c,104 d may be located in a second plane. Embodiments are well suited toother combinations of planes with respect to geolocations 104.

Contour of the Ground's Surface

Referring to FIGS. 1, 3 and 4, according to one embodiment, the contourof the ground's surface 114 is used as a part of determining where aradar signal 106 intersects 112 with the ground's surface 114, which inturn can be used for determining the length of the air path 108 for aradar signal 106. A topographical survey of the ground's surface 114 canbe used for determining the contour of the surface 114. According toanother embodiment, a topographical survey is not used and is notrequired. For example, the contour of the surface 114 of the ground maybe reasonably flat or may be reasonably well known. A road surface is anexample of a ground surface 114 that may be flat or reasonably wellknown.

Dielectric Constant

According to one embodiment, the informations for the different views ofan object 120 taken from different geolocations 104 are correlated witheach other to estimate one or more dielectric constants of the mediumbetween the ground's surface 114 and an object 120. According to oneembodiment, an estimation filter is used as a part of approximating thedielectric constant of the medium. Some non-limiting examples ofestimation filters include a Kalman filter and a least squares filter.Multiple variables may be fitted using the least squares filter.Examples of various variables include the dielectric constant, thecontour of the surface 114 of the ground, among others. An a prioridielectric constant for the ground is used as a starting point.

In another embodiment, a synthetic aperture realization may be employed,wherein the synthetic aperture algorithm is augmented so that thedifferent radar views run simultaneously. In this embodiment, thedielectric constant is adjusted to maximize the agreement of the viewsand the focus of the synthetic apertures on the object.

Further, the medium may not be homogenous. For example, the medium mayhave layers of different types of materials. More specifically, themedium may have respective layers of asphalt, followed by gravel, thendirt. The medium may have a layer of clay. These are just a few examplesof the different types of materials that may be found in the medium thatmake it heterogeneous. Each type of material or layer may have adifferent dielectric constant. Therefore, another variable that may befitted may be the dielectric constant. The dielectric constants of therespective materials or layers can be used to determine the velocity ofa radar signal when it traveled through that material or layer. Forexample, if infrastructure below a road surface is being explored, theroad surface will have a reasonably well-known thickness, which can beverified with the radar, and dielectric constant.

Image of an Object

According to one embodiment, one or more characteristics of the object120 can be used as a part of locating the object 120. After processingthe radar data, the estimate of object surface will consist of acollection of positionally identified points underground—a “pointcloud.” The position estimate can be improved if the further adjustmentof dielectric constant and other parameters, such as dielectric layerthickness, that were used to create the point cloud is done to improveconformance between the point cloud and the known shape of the object.In a specific example, if it is known that the object 120 is a pipe,then a feedback component can be implemented to adjust the dielectricconstant and other parameters so that the image of a pipe best matchingto the resulting point cloud. The resulting point cloud, following theadjustment(s) will have better accuracy.

Large Aperture and Synthetic Aperture Radar

According to one embodiment, a large aperture is used as a part ofdetermining a view of an object 120 from a geolocation 104. According toone embodiment, a large aperture can be synthesized. Various techniquescan be used for synthesizing a large aperture. One technique involvesusing a single radar head and moving that single radar head around.Another technique involves using a multiple antennae array.

FIGS. 6 and 7 depict two different types of devices that can be used forsynthesizing a large aperture, according to various embodiments. Device600 includes a single radar head 102 that can be moved to any positionin a matrix defined by a rectangle 610 as indicated by the x′-axis andthe y′-axis. For example, the single radar head 102 could be moved sideways on a boom in the x′-axis. Further, the radar head 102 may be movedup and down, for example, by moving the boom up and down in the y′-axis.Radar signals can be transmitted from and then received at any of thepositions in the matrix defined by the rectangle 610.

Device 700 includes multiple antennas 710 that are located at variouspositions in a matrix defined by a rectangle as indicated by the x″-axisand the y″-axis. A first subset of the antennas 710 are transmittingantennas and a second subset of the antennas 710 are receiving antennas.Radar signals can be transmitted from any of the transmitting antennasand then received at any of the receiving antennas associated withdevice 700.

Either device 600 or 700 could be positioned at any of the geolocations104 depicted in FIG. 1, 3 or 4 to determine a view from any of therespective geolocations 104.

An Example of a System

FIG. 8 depicts a block diagram of a system 800 for detecting an objectthat is under the ground, according to one embodiment. The blocks thatrepresent features in FIG. 8 can be arranged differently than asillustrated, and can implement additional or fewer features than whatare described herein. Further, the features represented by the blocks inFIG. 8 can be combined in various ways. The system 800 can beimplemented using hardware, hardware and software, hardware andfirmware, or a combination thereof.

The system 800, as depicted in FIG. 8, includes a transmitting radarantennae 210 a and a receiving radar antennae 210 b. The system 800 alsoincludes a view-determining-component 810 and aposition-estimating-component 820. The view-determining-component 810 isconfigured for determining a first view of the object 120, which is atleast partially under the surface 114 of the ground, by transmitting afirst radar signal 106 a from a first known geolocation 104 a and fordetermining a second view of the object 120 by transmitting a secondradar signal 106 b from a second known geolocation 104 b, whereinrespective trajectories 108 a, 108 b of the first and second radarsignals 106 a, 106 b are oblique with respect to the surface 114 of theground and the respective trajectories 108 a, 108 b are at an angle 116a with respect to each other. The position-estimating-component 820 isconfigured for approximating a dielectric constant associated withmedium between the object 120 and the surface 114 of the ground bycorrelating information pertaining to the first view and the secondview. According to one embodiment, a dielectric constant that isassociated with the medium could be a dielectric constant for ahomogenous medium a collection of dielectric constants for the layers ofmaterial for a heterogeneous medium. In some embodiments,position-estimating-component 820 further utilizes one or more objectmodels to enhance position estimates. For example, when the nature of anunderground object is known in advance, a model of that object can beused to better fit the data obtained from the reflected radar signals.Consider an example where it is known from some source such as ablueprint or a geographic information system that the actual undergroundobject being searched for is a sewer pipe. In such a situation, becauseit is known in advance that the collected data points should conform tothe shape of a cylindrical sewer pipe, position-estimating-component 820utilizes a model of a cylindrical shape when correlating informationpertaining to the first and second view (and any additional views) ofthe actual object. In a similar fashion, models of other known objectsmay also be employed.

The components 210 a, 210 b, 810, 820 may be located in the sameelectronic device or any number of different electronic devices.

An Example of a Method

FIG. 9 is a flow chart 900 of a method of detecting an undergroundobject, according to one embodiment. Although specific operations aredisclosed in flowchart 900, such operations are exemplary. That is,embodiments of the present invention are well suited to performingvarious other operations or variations of the operations recited inflowchart 900. It is appreciated that the operations in flowchart 900may be performed in an order different than presented, and that not allof the operations in flowchart 900 may be performed.

For the sake of illustration, refer to FIGS. 1, 2 and 5 for thefollowing description of flowchart 900.

At 910, the method begins.

At 920, a first view of the object 120, which is at least partiallyunder the ground's surface 114, is determined by transmitting a firstradar signal 106 a from a first known geolocation 104 a. For example, afirst radar signal 106 a is transmitted by a transmitting radar antennae210 a from a first geolocation 104 a. The time that a radar signal 106is transmitted is referred to as “time of transmission.” According toone embodiment, the angle 118 a between the first radar signal 106 a andthe ground surface 114 is approximately a Brewster angle in order tomaximize the power of the first radar signal 106 a entering the ground.

The first radar signal 106 a travels along an air path 108 a until itintercepts the surface 114 of the ground at location 112 a. Informationpertaining to the contour of the ground can be used as a part ofestimating the location 112 a of interception, as discussed herein. Theearth path 110 a of the first radar signal 106 a is from location 112 ato the object 120 at location 113 a. Since the first radar signal 106 atransitions from traveling through the air to traveling through theground, the first radar signal 106 a is reflected and the angle oftransmission for the earth path 110 a is different than the angle oftransmission for the air path 108 a.

The first radar signal 106 a bounces off of the object 120 and isintercepted by a receiving radar antennae 210 b. The time that a radarsignal 106 a is received by the receiving radar antennae 210 b isreferred to as “time of reception.”

At 930, a second view of the object 120 is determined by transmitting asecond radar signal 106 b from a second known geolocation 104 b.

For example, a second radar signal 106 b is transmitted by thetransmitting radar antennae 210 a from a second geolocation 104 b.According to one embodiment, the angle 118 b between the second radarsignal 106 b and the ground surface 114 is approximately a Brewsterangle in order to maximize the power of the second radar signal 106 bentering the ground.

The second radar signal 106 b travels along an air path 108 b until itintercepts the surface 114 of the ground at location 112 b. Informationpertaining to the contour of the ground's surface 114 can be used as apart of estimating the location 112 b of interception, as discussedherein. The earth path 110 b of the second radar signal 106 b is fromlocation 112 b to the object 120 at location 113 b. Since the secondradar signal 106 b transitions from traveling through the air totraveling through the ground, the second radar signal 106 b is reflectedand the angle of transmission for the earth path 110 b is different thanthe angle of transmission for the air path 108 b.

The second radar signal 106 b bounces off of the object 120 and isintercepted by the receiving radar antennae 210 b.

The respective trajectories of the air paths 108 a, 108 b of the firstand second radar signals 106 a, 106 b are, according to one embodiment,oblique with respect to the surface 114 of the ground. For example, thetrajectories of the air paths 108 a, 108 b of the first and second radarsignals 106 a, 106 b are not perpendicular with respect to the surface114 of the ground.

Referring to FIG. 5, the respective trajectories of the air paths 108 a,108 b are at an angle 116 a with respect to each other. For example, theangle 116 a between the trajectories of the respective air paths 108 a,108 b is approximately 90 degrees, according to one embodiment.

At 940, referring to FIGS. 1 and 2, a position of the object isestimated from the dielectric constant of medium between the object 120and the surface 114 of the ground. This position of the object isestimated by maximizing the correlation of information pertaining to thefirst view and the second view by adjusting an estimated dielectricconstant(s) of the medium. According to one embodiment, the medium isbetween the surface 114 of the ground at locations 112 a and 112 b andrespective locations 113 a and 113 b of the object 120 along therespective earth paths 110 a, 110 b. According to one embodiment, adielectric constant that is associated with the medium could be adielectric constant for a homogenous medium or a collection ofdielectric constants for the layers of material for a heterogeneousmedium.

According to one embodiment, information describing each of the views isobtained. For example, the information describing a view includes, amongother things, the angle 118 that a radar signal 106 was transmitted withrespect to the surface 114 of the ground, the length of the air path 108for that radar signal 106, and the amount of time from transmissionuntil reception of the transmitted radar signal 106.

The contour of the ground, as discussed herein, can be used as a part ofestimating where a radar signal 106 intercepted 112 the ground's surface114, and therefore, can be used in estimating the length of an air path108. According to one embodiment, a topographical survey of the ground'ssurface 114 is used as a part of determining the contour of the surface114. According to another embodiment, a topographical survey is not usedand is not required. For example, the contour of the surface 114 of theground may be reasonably flat or reasonably well known.

The information describing each of the views can be used to estimate oneor more dielectric constants associated with the medium between theground's surface 114 and the object 120. According to one embodiment, anestimation filter is used as a part of approximating the dielectricconstant of the medium. Some non-limiting examples of estimation filtersinclude a Kalman filter and a least squares filter. Multiple variablesmay be fitted using the least squares fitted filter. Examples of variousvariables include the dielectric constant, the contour of the surface114 of the ground, among others. Further, the medium may not behomogenous. For example, the medium may have layers of different typesof materials. More specifically, the medium may have respective layersof asphalt, followed by gravel, then dirt. The medium may have a layerof clay. These are just a few examples of the different types ofmaterials that may be found in the medium that make it heterogeneous.Each type of material may have a different dielectric constant.Therefore, another variable that may be fitted using an estimationalgorithm such as a least squares method may be the dielectric constantsfor the materials or layers of a heterogeneous medium.

A dielectric constant of a material or a layer can be used as a part ofestimating the velocity of a radar signal 106 through that material orlayer. The velocity of a radar signal 106 through a material or layer incombination with the angle 118 of the transmitted radar signal withrespect to the ground's surface 114 can be used to estimate how far theradar signal 106 traveled in a material or layer. In the case of aheterogeneous medium, the lengths that the radar signals 106 a, 106 btraveled in the respective materials or layers can be used as a part ofestimating the location of the object 120 in the ground. According toone embodiment, the location includes the depth of the object 120 belowthe ground's surface 114.

According to one embodiment, the position-estimating-component 820,depicted in FIG. 8, performs the processing described with respect to940.

At 950, the method ends.

According to various other embodiments, additional views of the object120 may be determined. For example, referring to FIG. 3, a third viewmay be taken from a third geolocation 104 c where the angle 116 bbetween the respective trajectories of the air paths 108 a, 108 c forthe first radar signal 106 a and the third radar signal 106 c isapproximately 180 degrees. Referring to FIG. 4, a fourth view may betaken from a fourth geolocation 104 d where the angle 116 c between therespective trajectories of the air paths 108 a, 108 d for the firstradar signal 106 a and the fourth radar signal 106 d is approximately270 degrees. These are just a few examples of additional views andrespective angles 116 b, 116 c that may be used.

Additional views as depicted in FIGS. 3 and 4, or a combination thereof,can be processed in a similar manner as the first view and the secondview described in the context of FIG. 1 and flowchart 900 of FIG. 9.

Computer Readable Storage Medium

Any one or more of the embodiments described herein can be implementedusing radar transmitting and receiving hardware, along withnon-transitory computer readable storage medium and computer-executableinstructions which reside, for example, in computer-readable storagemedium of a computer system or like device. The non-transitory computerreadable storage medium can be any kind of memory that instructions canbe stored on. Examples of the non-transitory computer readable storagemedium include but are not limited to a disk, a compact disk (CD), adigital versatile device (DVD), read only memory (ROM), flash, and soon. As described above, certain processes and operations of variousembodiments of the present invention are realized, in one embodiment, asa series of instructions (e.g., software program) that reside withinnon-transitory computer readable storage memory of a computer system andare executed by the computer processor of the computer system. Whenexecuted, the instructions cause the computer system to implement thefunctionality of various embodiments of the present invention. Accordingto one embodiment, the non-transitory computer readable storage mediumis tangible.

CONCLUSION

Although various embodiments were described in the context of moving aradar head or a device from one geolocation to another geolocation,embodiments are well suited to using different radar heads or devices ateach of the geolocations so that the radar heads or devices are notmoved. Various embodiments are well suited for taking the differentviews simultaneously or at approximately the same time.

Various embodiments do not use or do not require any portion of theobject to be exposed above the ground's surface. However, variousembodiments are well suited for a portion of the object to be exposedabove the ground's surface.

Various embodiments do not use or do not require a radar signal to betransmitted perpendicularly to the ground's surface. Various embodimentsdo not use or do not require a radar signal to be transmitted close tothe ground's surface.

Example embodiments of the subject matter are thus described. Althoughthe subject matter has been described in a language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

Various embodiments have been described in various combinations andillustrations. However, any two or more embodiments or features may becombined. Further, any embodiment or feature may be used separately fromany other embodiment or feature. Phrases, such as “an embodiment,” “oneembodiment,” among others, used herein, are not necessarily referring tothe same embodiment. Features, structures, or characteristics of anyembodiment may be combined in any suitable manner with one or more otherfeatures, structures, or characteristics.

What is claimed is:
 1. A method of detecting an underground object, themethod comprising: determining a first view of the object, which is atleast partially under a surface of ground, by transmitting a first radarsignal from a first known geolocation; determining a second view of theobject by transmitting a second radar signal from a second knowngeolocation, wherein respective first and second trajectories of thefirst and second radar signals are oblique with respect to the surfaceof the ground and the respective first and second trajectories are at afirst angle with respect to each other; and estimating a position of theobject by maximizing a correlation between the first view and the secondview by adjusting an estimated dielectric constant associated withmedium between the object and the surface of the ground.
 2. The methodas recited by claim 1, wherein the determining of the second viewfurther comprises: determining the second view of the object bytransmitting the second radar signal from the second known geolocation,wherein the first angle between the first trajectory and the secondtrajectory is approximately 90 degrees.
 3. The method as recited byclaim 1, wherein the method further comprises: determining a third viewof the object by transmitting a third radar signal from a third knowngeolocation, wherein a third trajectory of the third radar signal isoblique with respect to the surface of the ground and the firsttrajectory and the third trajectory are at a second angle with respectto each other; and refining the estimated dielectric constant associatedwith the medium between the object and the surface of the ground bycorrelating information pertaining to the first view, the second view,and the third view.
 4. The method as recited by claim 3, wherein thedetermining of the third view further comprises: determining the thirdview of the object by transmitting the third radar signal from the thirdknown geolocation, wherein the second angle between the first trajectoryand the third trajectory is approximately 180 degrees.
 5. The method asrecited by claim 3, wherein the method further comprises: determining afourth view of the object by transmitting a fourth radar signal from afourth known geolocation, wherein a fourth trajectory of the fourthradar signal is oblique with respect to the surface of the ground andthe first trajectory and the fourth trajectory are at a third angle withrespect to each other; and refining the estimated dielectric constantassociated with the medium between the object and the surface of theground by correlating information pertaining to the first view, thesecond view, the third view, and the fourth view.
 6. The method asrecited by claim 5, wherein the determining of the fourth view furthercomprises: determining the fourth view of the object by transmitting thefourth radar signal from the fourth known geolocation, wherein the thirdangle between the first trajectory and the fourth trajectory isapproximately 270 degrees.
 7. The method as recited by claim 1, whereinthe method further comprises: transmitting the first radar signal andthe second radar signal at an angle with respect to the surface of theground that approximates a Brewster angle.
 8. The method as recited byclaim 1, wherein the method further comprises: determining a firstinterception of the first radar signal with the ground based oninformation describing a contour of the surface of the ground; anddetermining a second interception of the second radar signal with theground based on information describing the contour of the surface of theground.
 9. The method as recited by claim 8, wherein the method furthercomprises: determining a first length of a first air path based on thefirst angle and the first interception; and determining a second lengthof a second air path based on the first angle and the secondinterception.
 10. The method as recited by claim 9, wherein the methodfurther comprises: determining a first velocity of the first radarsignal through a first earth path based on the first length and thefirst angle; determining a second velocity of the second radar signalthrough a second earth path based on the second length and the firstangle; and determining the estimated dielectric constant based on thefirst velocity and the second velocity.
 11. The method as recited byclaim 1, wherein a medium between the surface of the ground and theobject comprises multiple layers of different types of material andwherein the method further comprises: determining a velocity that atleast one of the radar signals traveled through each of the layers; anddetermining estimated dielectric constants for each of the layers basedon the respective velocities for each of the layers.
 12. An system fordetecting an object that is underground, the system comprising: atransmitting radar antennae and a receiving radar antennae; aview-determining-component configured for determining a first view ofthe object, which is at least partially under a surface of ground, bytransmitting a first radar signal from a first known geolocation;determining a second view of the object by transmitting a second radarsignal from a second known geolocation, wherein respective trajectoriesof the first and second radar signals are oblique with respect to thesurface of the ground and the respective trajectories are at a firstangle with respect to each other; and a position-estimating-componentconfigured for estimating a position of the object by maximizing acorrelation between the first view and the second view by adjusting anestimated dielectric constant associated with medium between the objectand the surface of the ground.
 13. The system of claim 12, wherein thesystem further comprises: one or more synthetic aperture radar (SAR)devices configured for transmitting the first radar signal andtransmitting the second radar signal.
 14. The system of claim 12,wherein the position-estimating-component: employs a model of the objectas part of the actual object shape and location determination in orderto enhance position estimation of the object.
 15. The system of claim12, wherein the first radar signal and the second radar signal aretransmitted at an angle with respect to the surface of the ground thatapproximates a Brewster angle.
 16. The system of claim 12, wherein: theview-determining-component is further configured for determining a thirdview of the object by transmitting a third radar signal from a thirdknown geolocation, wherein a third trajectory of the third radar signalis oblique with respect to the surface of the ground and the firsttrajectory and the third trajectory are at a second angle with respectto each other; and the position-estimating-component is furtherconfigured for refining the estimated dielectric constant associatedwith the medium between the object and the surface of the ground bycorrelating information pertaining to the first view, the second view,and the third view.
 17. The system of claim 16, wherein: theview-determining-component is further configured for determining afourth view of the object by transmitting a fourth radar signal from afourth known geolocation, wherein a fourth trajectory of the fourthradar signal is oblique with respect to the surface of the ground andthe first trajectory and the fourth trajectory are at a third angle withrespect to each other; and the position-estimating-component is furtherconfigured for refining the estimated dielectric constant associatedwith the medium between the object and the surface of the ground bycorrelating information pertaining to the first view, the second view,the third view, and the fourth view.
 18. The system of claim 12,wherein: the view-determining-component is further configured fordetermining a first interception of the first radar signal with theground based on information describing a contour of the surface of theground; and the view-determining-component is further configured fordetermining a second interception of the second radar signal with theground based on information describing the contour of the surface of theground.
 19. The system of claim 18, wherein: theview-determining-component is further configured for determining a firstlength of a first air path based on the first angle and the firstinterception; and the view-determining-component is further configuredfor determining a second length of a second air path based on the firstangle and the second interception.
 20. The system of claim 19, whereinthe position-estimating-component is further configured for: determininga first velocity of the first radar signal through a first earth pathbased on the first length and the first angle; determining a secondvelocity of the second radar signal through a second earth path based onthe second length and the first angle; and determining the estimateddielectric constant based on the first velocity and the second velocity.21. The system of claim 20, wherein a medium between the surface of theground and the object comprises multiple layers of different types ofmaterial and wherein the position-estimating-component is furtherconfigured for: determining a velocity that at least one of the radarsignals traveled through each of the layers; and determining estimateddielectric constants for each of the layers based on the respectivevelocities for each of the layers.
 22. A non-transitory computerreadable storage medium having computer-executable instructions storedthereon for causing a computer system to perform a method of detectingan underground object, the method comprising: determining a first viewof the object, which is at least partially under a surface of ground,based on transmission of a first radar signal from a first knowngeolocation; determining a second view of the object based ontransmission of a second radar signal from a second known geolocation,wherein respective first and second trajectories of the first and secondradar signals are oblique with respect to the surface of the ground andthe respective first and second trajectories are at a first angle withrespect to each other; and estimating a position of the object bymaximizing a correlation between the first view and the second view byadjusting an estimated dielectric constant associated with mediumbetween the object and the surface of the ground.
 23. The non-transitorycomputer readable storage medium of claim 22, wherein the determining ofthe second view further comprises: determining the second view of theobject based on transmission of the second radar signal from the secondknown geolocation, wherein the first angle between the first trajectoryand the second trajectory is approximately 90 degrees.
 24. Thenon-transitory computer readable storage medium of claim 22, wherein themethod further comprises: determining a third view of the object basedon transmission of a third radar signal from a third known geolocation,wherein a third trajectory of the third radar signal is oblique withrespect to the surface of the ground and the first trajectory and thethird trajectory are at a second angle with respect to each other; andrefining the estimated dielectric constant associated with the mediumbetween the object and the surface of the ground by correlatinginformation pertaining to the first view, the second view, and the thirdview.
 25. The non-transitory computer readable storage medium of claim24, wherein the determining of the third view further comprises:determining the third view of the object based on transmission of thethird radar signal from the third known geolocation, wherein the secondangle between the first trajectory and the third trajectory isapproximately 180 degrees.
 26. The non-transitory computer readablestorage medium of claim 25, wherein the method further comprises:determining a fourth view of the object based on transmission of afourth radar signal from a fourth known geolocation, wherein a fourthtrajectory of the fourth radar signal is oblique with respect to thesurface of the ground and the first trajectory and the fourth trajectoryare at a third angle with respect to each other; and refining theestimated dielectric constant associated with the medium between theobject and the surface of the ground by correlating informationpertaining to the first view, the second view, the third view, and thefourth view.
 27. The non-transitory computer readable storage medium ofclaim 26, wherein the determining of the fourth view further comprises:determining the fourth view of the object based on transmission of thefourth radar signal from the fourth known geolocation, wherein the thirdangle between the first trajectory and the fourth trajectory isapproximately 270 degrees.
 28. The non-transitory computer readablestorage medium of claim 22, wherein the method further comprises:determining a first interception of the first radar signal with theground based on information describing a contour of the surface of theground; and determining a second interception of the second radar signalwith the ground based on information describing the contour of thesurface of the ground.
 29. The non-transitory computer readable storagemedium of claim 28, wherein the method further comprises: determining afirst length of a first air path based on the first angle and the firstinterception; and determining a second length of a second air path basedon the first angle and the second interception.
 30. The non-transitorycomputer readable storage medium of claim 29, wherein the method furthercomprises: determining a first velocity of the first radar signalthrough a first earth path based on the first length and the firstangle; determining a second velocity of the second radar signal througha second earth path based on the second length and the first angle; anddetermining the estimated dielectric constant based on the firstvelocity and the second velocity.
 31. The non-transitory computerreadable storage medium of claim 22, wherein a medium between thesurface of the ground and the object comprises multiple layers ofdifferent types of material and wherein the method further comprises:determining a velocity that at least one of the radar signals traveledthrough each of the layers; and determining the estimated dielectricconstants for each of the layers based on the respective velocities foreach of the layers.